1. FIELD OF THE INVENTION
This invention relates to a data receiving apparatus and a data receiving method, and more particularly, is applicable to a communication terminal of a digital portable telephone system and a method of receiving a data in the communication terminal.
2. DESCRIPTION OF THE RELATED ART
In recent years, the Code Division Multiple Access (CDMA) mode is known as a scheme of wireless connection between the base station and a communication terminal of a digital portable telephone system.
The CDMA mode has been standardized (Standard IS-95) by Telecommunications Industry Association (TIA), and prescribed that one species of transmission rate should be used in the radio section between a base station and a communication terminal (hereinafter, this is referred to as the radio transmission rate) and, as to transmission processing of the data at the inside of the communication terminal, a transmission processing rate which is suited for the quality of the circuit and the quality of the data, etc. should be selected and used out of the plural species of transmission rates (hereinafter, these are referred to as the trans mission processing rates) which are 1/n of the radio transmission rate ("n" are arbitrary integers).
Besides, the CDMA mode has bee n prescribed that, when the data is transmitted from the communication terminal, the data which is comprised of the consecutive plural symbols can be transmitted such that the symbols are regularly thinned out on the basis of the punctured Viterbi decoding mode, so that the data quantity which is transmitted can be decreased and the transmission efficiency can be improved.
Moreover, the CDMA mode has been prescribed that, when the data is transmitted from the communication terminal, the symbol of the stated position of the data which is comprised of the consecutive symbols can be replaced by, for instance, the control information of the transmission power (that is, power control bits) which has the same number as this and then transmitted. Thus, the receiving side is caused to control the transmission power on the basis of the control information and transmission of the radio section is optimized.
In the case where the symbol of the stated position of the data is replaced by the control information and then transmitted, the communication terminal performs convolutional coding with respect to the data which is the object of transmission, interleaves the resultant coded data, replaces the symbols of the different random positions selected for every stated number of symbols by the control information, and then transmits it.
A communication terminal which has received such a data has previously stored the information of the position where replacement by the control information has been performed (hereinafter, this is referred to as the replaced position information), and demodulates the received data into the soft decision symbols, and then takes out the control information from the demodulated data which has been thus obtained on the basis of the replaced position information. However, if the remaining data after the control information is taken out from the demodulated data is less than the original data, it is difficult to obtain the correct result of Viterbi decoding by using the remained data.
Therefore in this case, in the communication terminal, disappearance information which represents that the original symbols have disappeared owing to the control information is once stored in the storage circuit, along with the demodulated data whose control information has been taken out. In this state, de-interleaving is performed by reading out the respective symbols of the demodulated data, which has been stored in the storage circuit, in an order different from the order of storing, and by inserting the disappearance information in the positions at which the control information has been taken out (hereinafter, these are referred to as the disappeared symbol positions) at the time of said reading out, and then Viterbi decoding is performed on thus obtained data whose data quantity is equivalent to that of the original data.
By the way, in such a communication terminal, a translation table or an arithmetic circuit is required for reading out the demodulated data and the disappearance information which have been stored in the storage circuit, for inserting the disappearance information in the disappeared symbol positions while de-interleaving, and for translating the replaced position information into the new replaced positions which have been de-interleaved, so there has been such a problem that the scale of the circuit for executing disappearance treatment is large.
Besides, in the communication terminal, in the case of receiving data where the number of bits of each symbol of the received data is relatively large, a comparatively large capacity of storage circuit is required in response to the number of bits of the symbol, since the demodulated data and the disappearance information are stored in the storage circuit at the time of de-interleaving. There has been such a problem that the scale of the circuit for executing disappearance treatment is further enlarged in such a case.